Question

I am developing an application that allows the user at a certain point to drag and drop 10 images around. So there are 10 images, and if he/she drags one image onto another, these two are swapped.

A screenshot of how this looks like:

So when the user drags one photo I want it to reduce its opacity and give the user a draggable image on his finger which disappears again if he drops it outside of any image.

The way I have developed this is the following. I have set a UIPanGesture for these UIImageViews as:

for (UIImageView *imgView in editPhotosView.subviews) {
        UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(photoDragged:)];
        [imgView addGestureRecognizer:panGesture];

        imgView.userInteractionEnabled = YES;

        [panGesture release];
}

Then my photoDragged: method:

- (void)photoDragged:(UIPanGestureRecognizer *)gesture {

    UIView *view = gesture.view;
    if ([view isKindOfClass:[UIImageView class]]) {
        UIImageView *imgView = (UIImageView *)view;
        if (gesture.state == UIGestureRecognizerStateBegan) {
            imgView.alpha = 0.5;

            UIImageView *newView = [[UIImageView alloc] initWithFrame:imgView.frame];
            newView.image = imgView.image;            
            newView.tag = imgView.tag;
            newView.backgroundColor = imgView.backgroundColor;
            newView.gestureRecognizers = imgView.gestureRecognizers;

            [editPhotosView addSubview:newView];            
            [newView release];
        }
        else if (gesture.state == UIGestureRecognizerStateChanged) {
            CGPoint translation = [gesture translationInView:view.superview];
            [view setCenter:CGPointMake(view.center.x + translation.x, view.center.y + translation.y)];
            [gesture setTranslation:CGPointZero inView:view.superview];
        }
        else { ... }
    }
}

Thus as you see I add a new UIImageView with 0.5 opacity on the same spot as the original image when the user starts dragging it. So the user is dragging the original image around. But what I want to do is to copy the original image when the user drags it and create a “draggable” image and pass that to the user to drag around.

But to do that I have to pass the user touch on to the newly created “draggable” UIImageView. While it’s actually set to the original image (the one the user touches when he starts dragging).

So my question is: How do I pass the user’s touch to another element?.

I hope that makes sense. Thanks for your help!

Answer 1

In the end I decided to indeed drag the original image and leave a copy at the original place.

I solved the issue with the gesture recognizers I was having by re-creating them and assigning them to the “copy”, just like PragmaOnce suggested.